Abstract:

A method of manufacturing a biodiesel fuel that comprises generating
micro-droplets of a first reactant and mixing the micro-droplets of the
first reactant with a second reactant that is substantially immiscible
with the first reactant. The method also comprises transferring the
mixture of the first reactant and second reactant into a
transesterification reaction vessel. The first reactant is one of an
alcohol or oil, and the second reactant is the other of the oil or the
alcohol.

Claims:

1. A method of manufacturing a biodiesel fuel, comprising:generating
micro-droplets of a first reactant;mixing said micro-droplets of said
first reactant with a second reactant that is substantially immiscible
with said first reactant;transferring said mixture of said first reactant
and second reactant into a reaction vessel; andforming a biodiesel fuel
in said reaction vessel by a transesterification reaction,wherein said
first reactant is one of an alcohol or an oil, and said second reactant
is the other of said oil or said alcohol.

2. The method of claim 1, wherein said micro-droplets have an average
diameter in a range of about 20 to 100 microns.

3. The method of claim 1, wherein generating said micro-droplets includes
stirring said mixture using a low-shear mixer.

4. The method of claim 1, wherein generating said micro-droplets includes
passing a liquid of said first reactant through one of an ultrasonic
atomizer, pressure atomizer or pneumatic atomizer to thereby produce said
micro-droplets.

5. The method of claim 1, wherein said transesterification reaction is
performed at a temperature above a normal boiling point of said alcohol.

6. The method of claim 1, further including flowing said reactant mixture
through a tubular reactor of said reaction vessel at an elevated
pressure.

7. A method of manufacturing a biodiesel fuel, comprising:mixing a
co-solvent, a first reactant and a second reactant together in a mixing
chamber to form a homogeneous solution, wherein said first reactant and
said second reactant are substantially immiscible with each other in the
absence of said co-solvent; andtransferring said homogeneous solution
into a transesterification reaction vessel,wherein said first reactant is
one of an alcohol or an oil, and said second reactant is the other of
said oil or said alcohol.

8. The method of claim 7, wherein said co-solvent includes a biodiesel
fuel.

9. The method of claim 7, wherein said mixing is performed in a static
mixer.

10. The method of claim 7, wherein said transesterification reaction is
performed at a temperature above a normal boiling point of said alcohol.

11. The method of claim 7, further including flowing said reactant mixture
through a tubular reactor of said reaction vessel at an elevated
pressure.

12. A method of manufacturing a biodiesel fuel, comprising:performing a
transesterification reaction between a reactant mixture including alcohol
and oil at a temperature that is greater than a normal boiling point of
said alcohol;transferring biodiesel fuel and glycerol transesterification
reaction products and a remainder of said reactant mixture into a flash
tank;flashing vapors of said alcohol out of said flash tank;
andtransferring a remaining content of said flash tank into a separation
vessel,wherein said first reactant is one of an alcohol or an oil, and
said second reactant is the other of said oil or said alcohol.

13. The method of claim 12, further including holding said remaining
content in said separation vessel for less than about 0.5 hours to allow
said biodiesel fuel and said glycerol to substantially separate from each
other.

14. The method of claim 13, wherein said remaining content is maintained
at a temperature that is at least about 20.degree. C. lower than said
temperature that is greater than said normal boiling point of said
alcohol.

15. The method of claim 12, wherein said transesterification reaction is
performed at a temperature above said normal boiling point of said
alcohol.

16. The method of claim 12, further including flowing said reactant
mixture through a tubular reactor of said reaction vessel at an elevated
pressure.

17. The method of claim 12, further including collection said vapors of
said alcohol flashed out of said flash tank into a condenser tank, and
using said alcohol as part of said reactant mixture.

18. A biodiesel fuel manufacturing system, comprising:an atomizer
configured to generating micro-droplets from a first reactant passed
through said atomizer;a mixing vessel configured to receive said
micro-droplets of said first reactant and combine said micro-droplets
with a second reactant to form a reactant mixture; anda reaction vessel
configured to receive said reactant mixture and convert said reactant
mixture into a reaction product that includes a biodiesel fuel in a
transesterification reaction,wherein said first reactant is one of an
alcohol or an oil, and said second reactant is the other of said oil or
said alcohol, andwherein said first reactant is substantially immiscible
with said second reactant.

19. A biodiesel fuel manufacturing system, comprising:a mixing vessel
configured to form a homogeneous reactant solution of a co-solvent, an
alcohol and an oil;a delivery system configured to deliver said
co-solvent, said alcohol and said oil to said mixing vessel;a reaction
vessel configured to receive said homogeneous reactant solution and
convert said homogeneous reactant solution into a reaction product that
includes a biodiesel fuel in a transesterification reaction,wherein said
alcohol and said oil are substantially immiscible with each other in the
absence of said co-solvent.

20. A biodiesel fuel manufacturing system, comprising:a reaction vessel
configured to perform a transesterification reaction between a reactant
mixture that includes an alcohol and an oil, said reactant mixture being
at a temperature that is greater than the normal boiling point of said
alcohol;a flash tank fluidly coupled to said reaction vessel, said flash
tank configured to receive biodiesel fuel and glycerol
transesterification reaction products and remaining said reactant
mixture, wherein said flash tank includes a flush value configured to
allow flushing of vapors of said alcohol out of said flash tank; anda
separation vessel fluidly coupled to said flash tank, said separation
vessel configured to receive a remaining content of said flash tank into
said separation vessel.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application claims the benefit of U.S. Provisional Application
Ser. No. 61/242,540, filed on Sep. 15, 2009, to Uzi Mann, entitled,
"METHODS AND SYSTEMS TO PRODUCE BIODIESEL FUEL;" which are all commonly
assigned with this application and incorporated herein by reference in
their entirety.

TECHNICAL FIELD

[0002]The present disclosure is directed, in general, to biodiesel
manufacturing processes and systems to facilitate such manufacturing.

BACKGROUND

[0003]Biodiesel fuel is typically produced via transesterification, by
reacting various plant and animal oils and fats with low molecular weight
alcohols (e.g., methanol, ethanol). Often, the transesterification
reaction is catalyzed by adding bases (e.g., NaOH, KOH) to the alcohol,
and, using an excess amount of alcohol. Batch production processes often
include mixing the oil or fat, the alcohol, and the catalyst in a large
reaction tank. After a sufficient reaction time has passed, the biodiesel
fuel that is produced is separated from the other reaction product (e.g.,
glycerol) and the unreacted starting materials (e.g., alcohol and
catalyst).

[0004]The use of existing processes and systems, however, can result in
undesirably long reactions times to substantially complete the
transesterification reaction, or, can have unacceptably high inputs of
energy to speed up the reaction. Existing processes and systems can also
require an undesirably long time to separate the biodiesel fuel from the
other reaction products and the unreacted starting materials.

[0005]Accordingly, what is needed in the art is a biodiesel fuel
production method and system that does not suffer from the disadvantages
associated with conventional methods, as discussed above.

SUMMARY

[0006]To address the above-discussed deficiencies, the present disclosure
provides in one embodiment, a method of manufacturing a biodiesel fuel.
The method comprises generating micro-droplets of a first reactant and
mixing the micro-droplets of the first reactant with a second reactant
that is substantially immiscible with the first reactant. The method also
comprises transferring the mixture of the first reactant and second
reactant into a transesterification reaction vessel. The first reactant
is one of an alcohol or oil, and the second reactant is the other of the
oil or the alcohol.

[0007]Still another embodiment of the disclosure is another method of
manufacturing biodiesel fuel. The method comprises mixing a co-solvent, a
first reactant and a second reactant together in a mixing chamber to form
a homogeneous solution. The first reactant and the second reactant are
substantially immiscible with each other in the absence of the
co-solvent. The first reactant is one of an alcohol or oil, and the
second reactant is the other of the oil or the alcohol. The method
further comprises transferring the homogeneous solution into a
transesterification reaction vessel. The first reactant is one of an
alcohol or oil, and the second reactant is the other of the oil or the
alcohol.

[0008]Yet another embodiment of the disclosure is another method of
manufacturing biodiesel fuel. The method comprises performing a
transesterification reaction between a reactant mixture including alcohol
and oil at a temperature that is greater than the normal boiling point of
the alcohol. The method further comprises transferring biodiesel fuel and
glycerol transesterification reaction products and a remainder of the
reactant mixture into a flash tank. The method also comprises flashing
vapors of the alcohol out of the flash tank and transferring a remaining
content of the flash tank into a separation vessel. The first reactant is
one of an alcohol or oil, and the second reactant is the other of the oil
or the alcohol.

[0009]Another embodiment of the disclosure is a biodiesel fuel
manufacturing system. The system comprises an atomizer configured to
generate micro-droplets from a first reactant passed through the
atomizer. The system also comprises a mixing vessel configured to receive
the micro-droplets of the first reactant and combine the micro-droplets
with a second reactant to form a reactant mixture. The system further
comprises a reaction vessel configured to receive the reactant mixture
and convert the reactant mixture into a reaction product that includes a
biodiesel fuel in a transesterification reaction. The first reactant is
one of an alcohol or oil, and the second reactant is the other of the oil
or the alcohol. The first reactant is substantially immiscible with the
second reactant.

[0010]Yet another embodiment of the disclosure is another biodiesel fuel
manufacturing system. The system comprises a mixing vessel configured to
form a homogeneous reactant solution of a co-solvent, alcohol and oil.
The system also comprises a delivery system configured to deliver the
co-solvent, the alcohol and the oil to the mixing vessel. The system
further comprises a reaction vessel configured to receive the homogeneous
reactant solution and convert the homogeneous reactant solution into a
reaction product that includes a biodiesel fuel in a transesterification
reaction. The alcohol and the oil are substantially immiscible with each
other in the absence of the co-solvent.

[0011]Still another embodiment of the disclosure is another biodiesel fuel
manufacturing system. The system comprises a reaction vessel configured
to perform a transesterification reaction between a reactant mixture that
includes an alcohol and oil, the reactant mixture being maintained at a
temperature that is greater than a normal boiling point of the alcohol.
The system also comprises a flash tank fluidly coupled to the reaction
vessel. The flash tank is configured to receive biodiesel fuel and
glycerol transesterification reaction products and remaining the reactant
mixture. The flash tank can be configured to flash vapors of the alcohol
out of the flash tank. The system also includes a separation vessel
fluidly coupled to the flash tank, the separation vessel configured to
receive a remaining content of the flash tank into the separation vessel.

[0012]Another aspect of the present disclosure is a biodiesel fuel that is
manufactured by anyone of the above described methods or systems.

[0013]The foregoing has outlined preferred and alternative features of the
present disclosure so that those skilled in the art may better understand
the detailed description of the disclosure that follows. Additional
features of the disclosure will be described hereinafter that form the
subject of the claims of the disclosure. Those skilled in the art should
appreciate that they can readily use the disclosed conception and
specific embodiment as a basis for designing or modifying other
structures for carrying out the same purposes of the present disclosure.
Those skilled in the art should also realize that such equivalent
constructions do not depart from the scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]For a more complete understanding of the present disclosure,
reference is now made to the following detailed description taken in
conjunction with the accompanying FIGUREs. It is emphasized that various
features may not be drawn to scale. In fact, the dimensions of various
features may be arbitrarily increased or reduced for clarity of
discussion. Reference is now made to the following descriptions taken in
conjunction with the accompanying drawings, in which:

[0015]FIG. 1 illustrates by flow diagram, selected aspects of example
methods of manufacturing a biodiesel fuel according to the principles of
the present disclosure;

[0016]FIG. 2 presents a schematic diagram of an example system of the
disclosure for manufacturing biodiesel fuel, according to the principles
of the present disclosure;

[0017]FIG. 3 presents a schematic diagram of another example system of the
disclosure for manufacturing biodiesel fuel, according to the principles
of the present disclosure; and

[0018]FIG. 4 shows example reactions times for substantially completing
the transesterification reaction for different reactor volumes, using an
example method of manufacturing a biodiesel fuel according to the
principles of the present disclosure; and

[0019]FIG. 5 shows front and side views of an example configuration of a
mixing tank for contacting micro droplets of one reactant with the other
reactant, such as the mixing discussed in the context of FIG. 2.

DETAILED DESCRIPTION

[0020]The term oil as used herein refers to any glyceride of a fatty acid
(e.g., mono-, di-, or triglycerides) that is capable of being converted
into esters of the fatty acid by a transesterification reaction. The term
oil as used herein includes solid or liquid state material at room
temperature. The term oil as used herein can include oils from any of
animal, plant or synthetically-derived sources. The term alcohol as used
herein refers to one or more compounds in which a hydroxyl group, (--OH),
is attached to a saturated carbon atom. Methanol and ethanol are
non-limiting examples of suitable alcohols.

[0021]Aspects of the present disclosure benefit from the recognition that
biodiesel fuel is generated by a chemical reaction between a first
reactant (e.g., one of oil or alcohol) and a second reactant (e.g., the
other of alcohol or oil) that are substantially immiscible with each
other, and, that the reaction rate is transport limited. Therefore, the
reaction rate can be rate-limited by the interfacial area between the two
immiscible reactants. In some conventional reactors, this interfacial
area is often formed by a mechanical mixer (e.g. a shear agitator) that
generates droplets of one of these reactants in the other reactant. The
limited interfacial area limits the transesterification reaction rate.

[0022]Aspects of the present disclosure benefit from the recognition that
the interfacial area per unit volume of reactant mixture is inversely
proportional to the size of the droplets of the reactant that are
dispersed in the other reactant. In some small-volume reactors (e.g.,
volumes less that of about 40 liters), mechanical-mixing sufficient to
cause high shear can be readily achieved, and small droplets can thereby
be formed. In larger, production-size reactors (e.g., volumes of about
4000 liters or larger), however, the formation of similar sized small
droplets may not be practical because of the higher power costs
associated with achieving similar degrees of shear as in the small-volume
reactors. Consequently, the reaction rate in larger, production-size
reactors, provide much slower reaction rate than in small-volume
reactors. Thus, because longer reaction times are needed, the cost of
biodiesel fuel production is higher.

[0023]Some embodiments of the present disclosure address these problems by
generating a dispersion of fine micro-droplets for at least one of the
reactants (e.g., one of oil or alcohol reactants) in a mixing chamber
with the other reactant (e.g., the other of the alcohol or oil). The term
micro-droplet, as used herein, refers to a fluid droplet (e.g., liquid
droplets) of the first or second reactants that have an average diameter
of about 100 microns or less. This mixture with the micro-droplets
dispersed therein (e.g., in the other reactants) is then introduced into
a reaction vessel where a transesterification reaction occurs. Generating
a dispersion of fine micro-droplets of a reactant prior to the mixture
being introduced into a reaction vessel can substantially increase the
transesterification reaction rate as compared to the rate where the
reactants are only mechanically-mixed in the reaction vessel.

[0024]Other embodiments of the present disclosure address the
above-described problems by adding a co-solvent to make the first and
second reactants (e.g., alcohol and oil, respectively) more (and in some
cases, completely) miscible with each other. Because the miscibility
between the first and second reactants is increased, the
transesterification reaction rate is less (and in some embodiments, no
longer) transport-limited because there is direct contact between the two
reactants (e.g., without the presence of the above-described interfacial
area). Consequently, the rate of the transesterification reaction is
increased. In some preferred embodiments, the co-solvent is the biodiesel
fuel that would be produced from the transesterification reaction between
the first and second reactants.

[0025]A potential disadvantage of including a co-solvent such as biodiesel
in the reactant mixture is that the co-solvent can be an inert species
that occupies volume as it passes through reactor vessel. Therefore a
larger reactor volume may be required to achieve the desired reaction
time. In practice, however, this disadvantage is outweighed by the
enhanced reaction rate associated with eliminating the need for
generating large interfacial areas between the reactants.

[0026]Aspects of the present disclosure also benefit from the recognition
that conducting the transesterification reaction at higher temperatures
can greatly increase the rate of the reaction, at least when the reaction
is not transport limited. For the purposes of the present disclosure, a
higher temperature is defined as being at least about 5° C. higher
than the normal boiling point (e.g., the normal boiling point at 1
atmosphere of pressure) of the alcohol (or multiple different alcohols)
used as one of the reactants. In some conventional processes, where the
transesterification reaction is transport-limited, due, e.g., to the
small interfacial area between the two reactants, although such high
temperatures would be expected to substantially increase the intrinsic
reaction rate, the higher rate cannot be realized because of the
above-discussed transport limitation. Additionally, in some conventional
reaction processes, one may expect that the use of such high temperatures
is undesirable because of large amounts of energy that may be needed to
heat the reaction vessel (e.g., a production-size reaction vessel), or,
because undesirably bulky reaction vessels are needed to contain the high
pressures generated inside the vessel (e.g., thick vessel walls to
withstand higher pressures). Therefore one might expect there to be
little motive to spend the energy needed to produce such higher
temperatures. In light of the present disclosure, however, this
expectation is incorrect. The expectation is incorrect at least because
the transport limitations can be substantially overcome and because a
large portion of the heat added to the reactor can be recovered through
the heat exchanger.

[0027]Additionally, aspects of the present disclosure also benefit from
the recognition that the transesterification is a reversible, slightly
endothermic reaction. Hence, the conversion of the transesterification
reaction is limited by the reaction equilibrium. Conducting the
transesterification reaction at higher temperatures favorably shifts the
equilibrium towards the desired biodiesel fuel reaction product, thereby
enhancing the yield of biodiesel fuel.

[0028]Some embodiments of the present disclosure address the
above-described problems by using a tubular reaction vessel. The tubular
reactor can be configured to be uniformly heated along all, or a portion
of, the length of the reaction tube. The tubular reactor can also be
configured to withstand the high pressures (e.g., up to about 70
atmospheres) that can coincide with high temperatures. A benefit from
using high pressure is that the high pressure can prevent the evaporation
of the alcohol inside the reactor, and keep the alcohol mixed in the
reacting fluid. The reaction mixture transferred into the tubular
reaction vessel can be the above-described mixture with micro-droplets
dispersed therein, or, with the co-solvent included therein. Because the
transesterification reaction of such mixtures is much faster than in some
convention processes, the biodiesel fuel can be produced as the mixture
is continuously flowing through the tubular reaction vessel.

[0029]Aspects of the present disclosure also benefit from the recognition
that the use of high temperature reaction mixtures can improve the
separation of the biodiesel product from other reaction products, or,
remaining reactants. For instance, in some cases the use of a high
temperature reaction mixture enables the removal of the alcohol in a
step, prior to and different from, separating the biodiesel fuel from the
other reaction products. For example, in some embodiments, the unreacted
alcohol leaving the reaction vessel is removed to a flash tank. By
removing the excess unreacted alcohol from the material leaving in the
reaction vessel, the separation of the biodiesel product from glycerol in
a subsequent separation step is improved. It was discovered that in the
absence of the unreacted alcohol, the glycerol is more rapidly separated
from the other reaction products (including biodiesel), as compared to
cases where the alcohol was present. For instance, in some cases, the
separation can be substantially completed in minutes or a few hours
instead of a day or more.

[0030]By contrast, in some conventional processes, after the
transesterification reaction is substantially completed, the material
from the reaction vessel (including unreacted alcohol) is transferred to
a separation vessel. In the separation vessel the biodiesel fuel product,
other reaction products (e.g., glycerol) and remaining reactants (e.g.,
excess unreacted alcohol) are allowed to separate based upon their
different densities. Because the alcohol is dissolved in the glycerol
phase, thus reducing the density of this mixture, the biodiesel fuel
separation process can take a day or more, thereby slowing the rate of
producing the biodiesel fuel in a useable form.

[0031]Additionally, to re-use the unreacted alcohol, the alcohol should be
removed from the glycerol in a separate step, which in certain
conventional processes, requires additional heating and separation
procedures. Certain embodiments of the present disclosure address this
problem by condensing the alcohol vapor removed in the flash tank and
re-using this alcohol in subsequent biodiesel fuel manufacturing
processes, without the need for spending additional time and energy to
separate the alcohol and glycerol.

[0032]In some conventional processes, the excess alcohol is not removed
before separating the biodiesel fuel, because it is thought that in the
absence of the excess unreacted alcohol, the reverse of the
transesterification reaction would occur, thereby resulting in a loss in
the yield of biodiesel fuel. As part of present disclosure, however,
conditions were discovered where this reverse reaction doesn't
substantially occur.

[0033]As noted above, in some embodiments, the transesterification
reaction is carried out at a high temperature, and the temperature of the
material in the reaction vessel is above the normal boiling point of the
alcohol (e.g., the normal boiling point at 1 atmosphere pressure). After
completing the reaction, instead of transferring the content of the
reaction vessel directly to a conventional separation vessel, the content
is transferred to a flash tank.

[0034]The flash tank can be equipped with a flash valve that can be
configured to reduce the pressure to nearly atmospheric pressure,
resulting in the evaporation of the alcohol. The alcohol vapors can be
removed to a condenser. After substantially removing the unreacted
alcohol, the remaining material from the reaction vessel is transferred
to the separation vessel. In some embodiments, the remaining material can
be cooled by passing a stream of remaining material through a heat
exchanger which can use the heat from the remaining reactant material to
heat the mixture of reactants before being fed into the reactor. It is
thought that because the remaining material's temperature is reduced in
the flash tank, and in the optional heat exchange, and because the
glycerol and biodiesel fuel are rapidly separated from each other, the
reversal of the transesterification reaction does not substantially
occur.

[0035]FIG. 1 illustrates by flow diagram, selected aspects of example
methods of manufacturing a biodiesel fuel according to the principles of
the present disclosure. The method comprises a step 105 of generating
micro-droplets of a first reactant (e.g., one of alcohol or oil), and, a
step 110 of mixing the micro-droplets of the first reactant with a second
reactant (the other of oil or alcohol) that is substantially immiscible
with the first reactant. The term substantially immiscible as used herein
means that less than about 100 ml of the first reactant can be dissolved
in 1000 ml of the second reactant at a standard temperature of 20°
C. and 1 atmosphere pressure. The method also comprises a step 115 of
transferring the mixture of the first reactant and second reactant (e.g.,
with the micro-droplets dispersed therein) into a transesterification
reaction vessel.

[0036]In some embodiment, generating the micro-droplets in step 105 and
mixing the micro-droplets of the first reactant with a second reactant in
step 110 can be accomplished by stirring a mixture of the first reactant
and second reactant in the mixing vessel, e.g., using a low-shear mixer.
However, as discussed above, the energy efficient generation of
micro-droplets in this manner can sometimes be limited to volumes of
about 40 liters or less.

[0037]In some preferred embodiments, generating the micro-droplets in step
105 can include passing a liquid of the first reactant through an
atomizer to thereby produce micro-droplets. The atomizer can be an
ultrasonic atomizer, pressure atomizer, pneumatic atomizer, disc
atomizer, or other atomizers that are well-known to those skilled in the
art.

[0038]In some embodiments, it is advantageous to use an ultrasonic
atomizer because the power required to generate the micro-droplets is
lower than for other types of atomizers. In addition, ultrasonic
atomizers can generate narrowly-distributed droplets whose diameter is
easily controlled (e.g., by the atomizer frequency). Ultrasonic atomizers
can generate a lower velocity spray of micro-droplets, thus facilitating
the use of a smaller mixing volume space than some other types of
atomizers.

[0039]Using ultrasonic atomizer in the present disclosure is in contrast
to using ultrasonic device to vibrate the reactor vessel that has been
filled with the two liquid reactants of oil or fat plus alcohol.
Vibrating the reactor vessel itself sufficiently to increase the
transesterification reaction rate could become increasingly difficult and
more expensive as the reactor volume is increased. At some point, for
some very large reactors, it is expected that the energy required for the
vibration would exceed the energy value of the biodiesel fuel that is
produced.

[0040]As noted above, in cases where the transesterification rate is
transport limited, the size of the micro-droplets can strongly influence
the time needed to substantially complete the reaction. As also noted, it
is sometimes advantageous to use an ultrasonic atomizer in step 105,
because the ultrasonic atomizer can finely control the production of
micro-droplets to be within a narrow size range by adjusting the
vibrating frequency of the ultrasonic atomizer, and thereby control the
transesterification reaction. For example, the lower the frequency of
vibration, the larger the size of the micro-droplet. For example, in some
embodiments using a vibration frequency of about 20 kHz frequency, the
average diameter of micro-droplets can be with a narrow range of about 40
microns. For example, the micro-droplets can have an average diameter in
a range of about 40 to 100 microns, when a 20 kHz atomizer is used. For
example, using a higher frequency (e.g., about 40 kHz) can produce
micro-droplets with an average diameter of about 20 microns.

[0041]In some embodiments, it is advantageous to generate the
micro-droplets of alcohol in step 105. For instance, because alcohol
generally has a lower viscosity than oil, it can take relatively less
energy to pass large volumes of alcohol through one of the
above-described atomizers as compared to oil. In some embodiments, for
example, the first reactant of alcohol can be passed through the
ultrasonic atomizer at flow rates up to about 20 liters per minute. In
other embodiments, however, the oil can be heated to decrease its
viscosity and then passed through an atomizer to produce micro-droplets.
In still other embodiments, both micro-droplets of both the first or
second reactant (or both) can be generated in step 105.

[0042]In other embodiments, it can be advantageous to use a pressure
atomizer to generate the micro-droplets in step 105 because these types
of atomizers can be more energy efficient at processing higher flow rates
of the first reactant. For instance, the first reactant of alcohol can be
passed through the ultrasonic atomizer at flow rates of greater than 20
liters per minute. The size of the droplets can be controlled by
configured the opening of the nozzle of the pressure atomizer, although
the use of a smaller opening to produce smaller-sized droplets may limit
the flow rate. However, pressure atomizers with multiple nozzles can be
employed to increase the flow rate, if desired. The one potential
disadvantage of the pressure atomizers, however, is that a broader size
range of micro-droplets may be generated than when using an ultrasonic
atomizer. Alternatively, a pneumatic atomizer or a disc atomizer can be
used to handle high flow rates of the atomized liquid. Embodiments of the
pneumatic atomizer can be equipped with a side-inlet coupled into the
flow of the reactant through the nozzle, through which one can apply a
pressurized gas, such as air. The greater the flow of air through the
side-inlet, the smaller the size of the micro-droplet. One beneficial
feature of the disc atomizer is that its output of micro-droplets may
cover a very large volume, and so it can be more desirable to apply to
large volume mixing tanks (e.g., about 40 liters or more, and in some
cases 40,000 liters or more).

[0043]In some embodiments, the mixing step 110 includes stirring first
reactants and second reactants together to form a substantially uniform
dispersion of the micro-droplets of first reactants in the second
reactants. The term substantially uniform dispersion as used herein means
that the same concentration of droplets exists throughout the volume of
the dispersion. For instance, in some cases, the concentration of
droplets in the top 1/10 percent of the tank is the same (±10 percent)
as in the bottom 1/10 of the tank. In some preferred embodiments, mixing
is achieved using an external circulating pump. In other cases, the
mixing step 110 can be achieved using a mixing vessel having a stirring
blade, propeller or other moveable stirring means. In some cases, the
mixing vessel is a static mixer and mixing is achieved by static mixing.

[0044]FIG. 1 also illustrates another embodiment of the method, in which
there is no need for micro-droplet to be generated and mixed with the
other reactant, in accordance with steps 105 and 110. Such embodiments of
the method comprise a step 120 of mixing a co-solvent, a first reactant
and a second reactant together in a mixing chamber to form a homogeneous
solution. In some preferred embodiments, the co-solvent, a first reactant
and a second reactant are mixed in step 110 using a static mixer. Such
embodiments of the method also comprise the step 120 of transferring the
mixture of the first reactant and second reactant (e.g., the homogeneous
solution) into the transesterification reaction vessel.

[0045]The first reactant (e.g., one or alcohol or oil) and second reactant
(e.g., the other of oil or alcohol) are substantially immiscible with
each other in the absence of the co-solvent. The term homogenous solution
as used herein means that all components are retained in a single phase.
For instance, one or more of the components do not separate into
different phases even when the solution is left stationary for an
extended period of time (e.g., 24 hours). For instance, in some cases, a
homogenous solution is provided when at least one liter of the first and
second reactants (where the molar ratio of alcohol:oil is about 6:1) is
mixed with 2 liters of the co-solvent to form about 3 liters of the
homogenous solution, the mixing taking place at a temperature of about
20° C. and pressure of 1 atmosphere.

[0046]In some embodiments, the co-solvent includes or is a biodiesel fuel.
For instance, in some cases the biodiesel fuel used as the co-solvent is
a transesterification reaction product of the first reactant and the
second reactant. This has the advantage of not requiring additional steps
and expense to provide or recover the co-solvent. In other cases,
however, a different biodiesel fuel, produced from the
transesterification of different reactants, can be used as the
co-solvent. In view of the present disclosure, one skilled in the art
would appreciate that other types of co-solvent can be used.

[0047]In some embodiments, it is desirable for the initially formed
homogenous solution to be substantially free of glycerol (e.g., less than
0.01 moles of glycerol per mole of alcohol or oil). The presence of
glycerol in the homogenous solution could promote the reversal of the
transesterification reaction in the reaction vessel, thereby reducing
yields of biodiesel fuel production and the purity of the biodiesel fuel
product.

[0048]In some embodiments, the proportions of the first reactant of
alcohol and second reactant of oil are provided such that the mixture
transferred to the reaction vessel in step 115 has an alcohol:oil molar
ratio of at least about 3:1. In some embodiments it is desirable to have
a stoichiometric excess of alcohol because this can increase the rate of
the transesterification reaction and enhance the equilibrium conversion.
For instance, in some cases, the alcohol-to-oil molar ratio ranges from
more than about 3:1 to less than about 9:1, and more preferably, equal to
about 6:1.

[0049]FIG. 1 further illustrates that embodiments of the method can
further include a step 125 of forming the biodiesel fuel in the reaction
vessel by performing the transesterification reaction on a reactant
mixture. In some embodiments, the transesterification reaction in step
125 is performed at a standard temperature of 20° C. and pressure
of 1 atmosphere. In other embodiments, transesterification reaction in
step 125 is performed at a temperature that is greater than the normal
boiling point (e.g., the normal boiling point at 1 atmosphere pressure),
of the alcohol corresponding to the first or second reactant. In a sealed
reaction vessel, an elevated pressure (e.g., greater than 1 atmosphere),
that should be present concurrent with the elevated temperature, can help
to hold the alcohol in the liquid reactant mixture. For instance, some
embodiments of the transesterification reaction carried out in step 125
(e.g., using methanol as the first reactant) can be performed at a
temperature in the range from 70 to 150° C. and a pressure in the
range from about 2 to 20 atmospheres.

[0050]In some embodiments, the reactant mixture in the reaction vessel
also includes a catalyst such as a base (e.g., NaOH, KOH or similar
inorganic bases or organic bases). In some preferred embodiments, the
reactant of alcohol includes the catalyst. However, it is possible that
base can be separately introduced into the reaction vessel, or can be
included in the mixture transferred in step 115, or can be included with
the second reactant of oil.

[0051]In some embodiments forming the biodiesel fuel in step 125, includes
a step 130 of passing the mixture transferred in step 115, through a
tubular reactor of the reaction vessel. Benefits from using a tubular
reactor have been discussed elsewhere herein. In some embodiments, a
continuous flow rate of the reactant mixture through the tubular reactor
can be about 1.7 liters/minute and the tubular reactor can have a
diameter of about 0.08 meter and a length of about 7 meters.

[0052]FIG. 1 further illustrates that some embodiments of the method can
further include a step 135 of transferring the content of the reaction
vessel into a flash tank. For instance, the content of
transesterification reaction products (e.g., biodiesel fuel and glycerol)
and remaining reactant mixture are transferred in step 135.

[0053]Some embodiments of the method can also include a step 140 of
flashing vapors of the alcohol out of the flash tank. The alcohol is in a
vapor-phase because the temperature of the material from the reaction
vessel is still above the boiling point of the alcohol and the pressure
in the flash tank is reduced to near atmospheric pressure, e.g., by means
of the flash valve. In some cases, the vapor-phase alcohol can be
collected in a condenser tank and re-used as a reactant in future
transesterification reactions (e.g., re-used as part of the mixture
formed in step 110 or step 120). In some preferred embodiments (e.g.,
such as when the molar ratio of alcohol-to-oil equals about 6:1), the
alcohol content (e.g., moles of alcohol) remaining in the flash tank
after step 140 is reduced by at least about 50 percent as compared to the
material originally transferred into the reactor in step 125.

[0054]Some embodiments of the method can also include a step 145 of
transferring a remaining liquid-phase content of the flash tank into a
separation vessel. E.g., after substantially removing the alcohol, the
remaining material from the reaction vessel is transferred from the flash
tank to the separation vessel.

[0055]Some embodiments of the method can also include a step 150 of
holding the remaining content in the separation vessel for a duration of
time sufficient to allow the biodiesel fuel and the glycerol to
substantially separate from each other.

[0056]Typically, separation in step 150 can be achieved by gravity,
because glycerol has a density (e.g., about 1.3 gm/ml) that is
substantially greater than the density of biodiesel (e.g., about 0.9
gm/ml). The remaining content separates into a lower layer of glycerol
and upper layer of biodiesel fuel.

[0057]The duration of time needed to achieve separation in step 150 is
believed to be shorter than conventional separation steps because the
alcohol was substantially removed in step 140. By contrast, in some
conventional processes when the alcohol is still present, at least some
of the alcohol is dissolved in glycerol. This glycerol-plus-alcohol
mixture has a lower density than glycerol alone, and therefore separating
of the upper layer of biodiesel fuel from the lower layer of
glycerol-plus-alcohol proceeds slower than embodiments where the
incubation step 150 was preceded by the flashing step 140.

[0058]For instance, in some embodiments where the flashing step 140 and
transfer step 145 are performed, the holding step 150 includes a
separation period, by gravity, of less than 0.5 hours to achieve at least
about 90 percent separation of biodiesel fuel and said glycerol (by
volume) into two discernable layers.

[0059]In some embodiments, the reversal of the transesterification
reaction does not substantially occur during the holding step 150. For
instance, it is estimated that in some cases less than about 0.5 percent
of the biodiesel fuel is lost due to the reversal of the
transesterification reaction during the holding step 150. It is thought
that the reverse reaction does not substantially occur because the
temperature of the remaining material after removing the alcohol from the
flash tank (e.g., about 20° C. lower than the reactor temperature
in some cases), and subsequently transferred to the separation vessel
(e.g., about 40° C. lower than the flash tank temperature in some
cases), are reduced as compared to the temperature of the reaction
vessel, and because the glycerol and biodiesel fuel are rapidly separated
from each other in step 150. Thus, in some embodiments, the temperature
of the flash tank can be about 20° C. lower than the reactor
temperature, and the temperature of the separation tank can be about
40° C. lower than that in the flash tank.

[0060]In other embodiments of the method, however, the separation in step
150 can be performed directly after forming the biodiesel in step 130.
For instance, when the biodiesel is formed at about 20° C. in step
130, the flashing step 140 and transfer step 145 may not be performed,
and the holding step 150 by gravity can include a conventional holding
time of a day or more. While other methods (e.g., centrifugation, etc. .
. . ) could be used to speed the separation, such procedure may require
additional equipment and more energy than merited.

[0061]One skilled in the art would be familiar with additional steps that
the method could include, a step 155 of isolating of the biodiesel fuel
after the holding period, or, a step 160 of collecting liquid alcohol
that was removed in the flashing step 140.

[0062]Another embodiment of the disclosure is a system for manufacturing
biodiesel fuel. FIG. 2 presents a schematic diagram of an example system
200 of the disclosure for manufacturing biodiesel fuel, according to the
principles of the present disclosure. The system 200 comprises an
atomizer 205 (e.g., ultrasonic atomizer or other atomizers) configured to
generate micro-droplets from a first reactant 215 (e.g., one of an
alcohol or an oil, such as methanol, "MeOH") passed through the atomizer.
The system 200 also comprises a mixing vessel 210 (e.g., "Mixing Tank")
configured to receive the micro-droplets of the first reactant 215 and
combine the micro-droplets with a second reactant 217 (e.g., other of the
oil or the alcohol, oil) to form a reactant mixture 212 (e.g., a
dispersion mixture). The first reactant 215 is substantially immiscible
with the second reactant 217. In the depicted system 200, an external
circulating pump 225 coupled to the mixing vessel 210 facilitates the
mixing. The system 200 further comprises a reaction vessel 230 (e.g.,
Reactor) configured to receive the reactant mixture 220 (e.g.,
transferred via another circulating pump 225) and convert the reactant
mixture 220 into a reaction product 232 that includes a biodiesel fuel in
a transesterification reaction. In the depicted system 200, the reaction
vessel 230 includes or is a tubular reactor 234 and includes a heater
236. The depicted embodiment also includes a delivery system 240 (e.g.,
including pumps 242 and tubing 244) configured to deliver the alcohol 215
and the oil 217 to the mixing vessel 210.

[0063]FIG. 3 presents a schematic diagram of another example system 200 of
the disclosure for manufacturing biodiesel fuel. The system 200 comprises
a mixing vessel 210 (e.g., a static mixer) configured to form a
homogeneous reactant solution 212 (e.g., a single liquid phase) of a
co-solvent 310 (e.g., Biodiesel fuel), an alcohol 215 (e.g., methanol)
and an oil 217. The system 200 also comprises a delivery system 240
(e.g., pumps 242 and tubing 244) configured to deliver the co-solvent
310, the alcohol 215 and the oil 217 to the mixing vessel 210. The system
further comprises a reaction vessel 230 (e.g., including a tubular
reactor 234, and heater 236) configured to receive the homogeneous
reactant solution 212 and convert the homogeneous reactant solution 212
into a reaction product 232, that includes a biodiesel fuel, in a
transesterification reaction. The alcohol 215 and the oil 217 are
substantially immiscible with each other in the absence of the co-solvent
310.

[0064]FIGS. 2 and 3 also schematically illustrate aspects of another
example biodiesel fuel manufacturing system 200. The example system 200
comprises a reaction vessel 230 (e.g., including a tubular reactor 232)
configured to perform a transesterification reaction between a reactant
mixture that includes an alcohol 215 and an oil 217. The reactant mixture
212 is maintained at a temperature that is greater than the normal
boiling point of the alcohol (e.g., the normal boiling point at 1
atmosphere pressure). E.g., a heater 236 can be coupled to a portion or
the entire reaction vessel 230 (e.g., a portion of the tubular reactor
234) and configured to apply heating that is sufficient to maintain the
reactant mixture at a temperature level that is higher than the normal
boiling point of methanol.

[0065]The system 200 also comprises a flash tank 250 fluidly coupled to
the reaction vessel 230. E.g., tubing 252 and valve 255 are configured to
control the pressure of the reaction vessel and to control the flow of
the reacted material in the reaction vessel 230 to the flash tank 250.
The flash tank 250 is configured to receive biodiesel fuel and glycerol
transesterification reaction products and the remaining reactant mixture.
The flash tank 250 can include a flash valve 255 configured to reduce the
pressure thus facilitating flashing of vapors of the alcohol (e.g.,
methanol) out of the liquid in the flash tank 250. As shown for the
example systems 200 in FIGS. 2 and 3 a separation vessel 260 is fluidly
coupled (indirectly or directly) to the flash tank 250 (e.g., as aided
with pump 225). The separation vessel 260 is configured to receive a
remaining liquid content 262 of the flash tank 250 into the separation
vessel 260.

[0066]In some cases, the flash tank 250 is coupled to a condenser 270
(e.g., air condenser) that is configured to condense the alcohol vapor to
liquid alcohol (e.g. methanol). In some cases, the flash tank 250 is
configured to pass the remaining content 262 in the flash tank 250 (e.g.,
the content after removing alcohol) through a heat exchanger 280 and then
to the separation tank 260. The heat exchange 280 is configured to reduce
the temperature of the remaining content 262 from the flash tank 250 to
facilitate separation of the biodiesel fuel 280 and glycerol 282 reaction
products and to deter the reversal of transesterification.

[0067]Although a number of features of the disclosed systems are
separately discussed, one skilled in the art, in view of the present
disclosure would understand how to combine these various features into
one system.

[0068]One skilled in the art, in view of the present disclosure, would
also understand how various types of biodiesel fuel could be manufactured
by any of the disclosed methods or systems.

[0069]Having described certain aspects of present disclosure, it is
believed that additional features will become even more apparent by
reference to the following examples. It will be appreciated that the
examples are presented solely for the purpose of illustration and should
not be construed as limiting the disclosure. For instance, although the
studies described below may be carried out in a laboratory or pilot-plant
setting, based on the present disclosure one skilled in the art could
adjust specific numbers, dimensions and quantities up to appropriate
values for a full-scale plant setting.

EXAMPLES

[0070]Example data collected as part of the present disclosure is depicted
below to illustrate aspects of the above-described methods and systems of
the disclosure.

[0071]Some experiments were conducted using a laboratory-scale system that
atomized a first reactant of alcohol to form micro-droplets using an
ultrasonic atomizer which were sprayed into a mixing tank and mixing a
second reactant of oil using a low shear impeller. The dispersion of
micro-droplets of the first reactant in the second reactant was then fed
to a tubular reactor where the transesterification reaction took place.

[0072]FIG. 4 shows the reactions times for substantially completing the
transesterification reaction for different reactor volumes, using an
example method of manufacturing a biodiesel fuel using the
laboratory-scale system. Note that FIG. 4 depicts the reaction time,
which is the inverse of the reaction rate. As shown in FIG. 4, the
transesterification reaction rates obtained using the ultrasonic atomizer
for a broad range of reactor volumes ("example embodiment") were faster
by a factor 25 to 100 as compare to the same reaction ("Current
Technology"), carried out on the same reactants under the same
conditions, except using solely mechanically-mixed reactant mixtures.

[0073]Experimental pilot-plant systems were also constructed. Some
experiments were conducted using a pilot-plant system equipped with an
atomizer to form micro-droplets, such as discussed above in the context
of FIGS. 1 and 2. In one experiment, the average flow rate of oil to the
mixing tank was about 11.6 G/hr and the average flow rate of methanol
(e.g., with sodium hydroxide catalyst included) was about 3.8 G/hr. The
atomizer was an ultrasonic atomizer configured to operate at a vibration
frequency of about 20 kHz (Sonics and Materials, Inc.; Newton, Conn.).
The reaction vessel was a tubular reactor. The tubular reactor comprised
an about 20 foot length of stainless steel pipe (schedule 40) having an
outer diameter of about 3 inches. The first about 7 feet of the reactor
was heated with electric-resistive heaters. The average reactor
temperature at the outlet end of the reaction vessel was about
104° C.

[0074]The system was run a sufficient period for about 77 G of oil to pass
through the reaction vessel. The amount of glycerol collected from the
separation tank was about 5.5 G and the estimated conversion of oil to
biodiesel fuel was estimated to be about 97%.

[0075]The mixing vessel comprised an about 55 gallon stainless steel
barrel. A first reactant of methanol was atomized using the
above-described type of ultrasonic atomizer configured to vibrate
vertically in the barrel at 20 kHz. Methanol micro-droplets having an
average diameter of about 40 microns were formed. The ultrasonic atomizer
probe was 6 inch wide, about 4 inch tall, and the width of its tip was
0.5 inch. Methanol was introduced to the two sides of the probe by two
4-inch wide manifolds, each mounted next to the vibrating surfaces. The
tip of the probe was located at about 6 inches above the intersection
line of two inclined plates (see e.g., example embodiment of a mixing
tank shown in FIG. 5). A two-dimensional plume of micro-droplets was
generated at the tip of the probe. The plume of micro-droplets was
sprayed on two thin layers of the recycling dispersion (e.g., fluid oil
and alcohol micro-droplets) as the fluid move down onto two inclined
plates inside the vessel. Mixing of the methanol droplets into the
dispersion was achieved as the two liquid layers from the plates were
merged.

[0076]The moving thin liquid layer on each inclined plate of the mixer was
formed by passing the circulating fluid (from the circulating pump; see
e.g., FIG. 2) through a manifold mounted at the top of the plate. To
assure good mixing and feeding of the homogeneous dispersion to the
reactor, the circulating flow rate of the dispersion was maintained at
least 20 times higher than the flow rate of the fresh oil. E.g., in some
experiments, the circulation flow rate was about 60 times the flow rate
of the oil.

[0077]In one experiment, the average flow rate of oil to the mixing tank
was about 7.1 G/hr (44 L/hr) and the average flow rate of methanol (with
NaOH catalyst included) was about 2.5 G/hr (14 L/hr). The reaction vessel
was the same as the above-described tubular reactor. The average reactor
temperature at the outlet end of the reaction vessel was about
105.4° C. Average flow rate of the reactant mixture through the
reaction vessel was about 20.7 gal/h

[0078]The system was run a sufficient period for about 125 G of oil to
pass through the reaction vessel. The amount of glycerol collected from
the separation tank was about 9 G and the estimated conversion of oil to
biodiesel fuel was estimated to be about 97%.

[0079]Other experiments were conducted using a pilot-plant system equipped
with a mixing vessel that was configured as a static mixing vessel. The
static mixing vessel was configured to form a homogenous solution of a
biodiesel fuel co-solvent, an alcohol first reactant (e.g., methanol) and
a second reactant of oil, without applying movable mixing features inside
the vessel, such as agitators. Avoiding the need for movable mixing
features is expected to facilitate making full-plant scaled versions of
the system, because problems associated with mixing large volume of
liquids using moving mixing features are avoided.

[0080]Although the present disclosure has been described in detail, those
skilled in the art should understand that they can make various changes,
substitutions and alterations herein without departing from the scope of
the disclosure in its broadest form.